Many types of semiconductor manufacturing equipment include a chamber where processing of the wafers is performed. In certain processes, the chamber is maintained at reduced pressure, and the flow of gases into and out of the chamber is tightly controlled. Examples of elements configured to ensure a controlled flow of gases into such a chamber include but are not limited to mass flow controllers (MFCs), pumps, valves, and seals, which may operate in conjunction to maintain the processing chamber in the desired state. Processes that are sensitive to gas composition may depend on all of these elements working reliably. Where one or more of these components fails to function as expected, the effect on materials being processed within the chamber can be detrimental.
Large leaks in a chamber may be caused by such things as a failed valve or stuck MFC. Such events are generally detectable, and readily corrected by equipment engineers.
By contrast, smaller leaks may arise from more subtle failures, such as a cracked seal, or a valve not fitted sufficiently tightly. Such smaller leaks are often difficult to detect, and may go undetected for quite some time. However, changed composition of gas in the chamber resulting from such smaller leaks can be sufficient to ruin the wafer being processed. The near-invisibility of small leaks, combined with their effect on sensitive recipes, renders such small leaks a significant problem.
Still another type of problem may arise where gas is introduced into the environment of the chamber through a “virtual leak”. As used herein, a “virtual leak” refers to the generation of unwanted gas within the chamber itself. One example of such a virtual leak occurs due to outgassing from materials already present within the chamber, such as residue from previous processes. The gas resulting from such a virtual leak can also adversely affect the reliability of processes occurring within a chamber.
From the above, it is seen that improved techniques for detecting leaks in a vacuum chamber are desired.